There is a general need to further improve the voice recognition rate of a voice recognition unit disposed in a car navigation device or the like in a vehicle cabin under conditions in which engine noise, road noise, and other noises penetrate the vehicle cabin interior.
For example, in the system disclosed in Patent Literature 1, a plurality of microphones is arranged (in a planar or rectilinear shape) in a sun visor, the directionality of a single microphone matches the direction of a talker, and the directionality of another adjacent microphone matches a different direction away from the direction of the talker by a fixed angle. The adaptive signal processor of the system in Patent Literature 1 is generally an adaptive type (subtractive type) that subtracts the noise obtained by the single microphone from the voice obtain by the single microphone to increase the SN ratio and thereby contribute to an improvement in the voice recognition rate.
Also, in the system disclosed in e.g., Patent Literature 2, a plurality of microphones is arranged in an arcuate shape (in a planar or concave curved line shape), and the directionality of the microphones matches the direction of a sound source. The signal addition means of the system in Patent Literature 2 is an addition type which adds the voice (the distance from the sound source to the microphone is fixed) and noise (the distance from the noise source to the microphone is not fixed) obtained from the microphones, accentuates the voice and offsets the noise to increase the SN ratio, and thereby contributes to an improvement in the voice recognition rate.
However, the present inventors, as a result of studying patent literature 1 and 2, recognized that further improvement in the recognition ratio is required in a voice recognition unit in a vehicle cabin.
Additionally, as a result of studying the application of a voice recognition unit in a vehicle cabin to not only a car navigation device, but also to an air conditioner, an interior lighting device, and other devices, the present inventors recognized that an assistant may also be present in addition to the driver as occupants in a vehicle cabin, and that further improvement in the recognition ratio is required in order to allow voice operation by a plurality of occupants. In other words, in the system in Patent Literature 1, the voice of an assistant would be recognized as noise in the other microphones; and in the system in Patent Literature 2, the voice of an assistant would not match a sound source, and the voice of the assistant cannot be effectively accentuated by the plurality of microphones.